1. Field of the Invention
The present invention relates to an elevator having no machine room disposed above an elevator shaft and, more specifically to an improved elevator capable of reducing the vertical height of a top space of the elevator shaft and of stably suspending an elevator cage.
2. Description of Related Art
Various elevators having no machine room disposed above an elevator shaft have been developed and proposed for the efficient utilization of space in buildings and for observing regulations regarding a right to sunshine.
FIGS. 6 and 7 show an elevator 1 previously proposed by the applicant of the present patent application in JP-A 157762/1999. This elevator 1 was developed to reduce the height of the top space of the elevator shaft and to reduce the horizontal cross section of the elevator shaft.
In this elevator 1, a pair of connecting beams 6 is horizontally extending between the upper ends of a pair of cage guide rails 3 for guiding the vertical movement of an elevator cage 2 and the upper ends of a pair of counterweight guide rails 5 for guiding a vertical movement of a counterweight 4 respectively. A drive unit 9 is mounted on a support beam 8 that extends horizontally between the upper ends of a pair of counterweight guide rails 5, in the vicinity of the inner side surface 7a of an elevator shaft 7.
A pair of drive shafts 11R and 11L projects from a hoist 10 included in the drive unit 9. A pair of traction sheaves 12R and 12L are mounted on the pair of drive shafts 11R and 11L, respectively. A pair of hoist cables 13R and 13L are wound around the pair of traction sheaves 12R and 12L, respectively.
One ends of the pair of hoist cables 13R and 13L are hitched directly to the elevator cage 2 by means of hitching devices 14, and the other ends are hitched directly to the counterweight 4 by means of hitching devices 15.
Referring to FIG. 7 which shows a top plan view of the elevator 1, the traction sheaves 12R and 12L are disposed in a space between the right inner side surface 7R of the elevator shaft 7 and the right vertical outer side wall 2R of the elevator cage 2, and a space between the left inner side surface 7L of the elevator shaft 7 and the left vertical outer side wall 2L of the elevator cage 2, respectively.
Therefore, the traction sheaves 12R and 12L do not interfere with the elevator cage 2 when the elevator cage 2 exists at the top portion of the elevator shaft 7. Consequently, the vertical height of the top space and the horizontal cross section of the elevator shaft 7 can be reduced.
However, in this elevator 1, the elevator cage 2 and the counterweight 4 are suspended by the pair of hoist cables 13R and 13L extending in so-called one-to-one roping arrangement, which is hitched directly to the elevator cage 2 and the counterweight 4 respectively.
Therefore, the hoist 10 must be capable of exerting a large torque and hence the hoist 10 has a comparatively big diameter.
Also the drive unit 9 including the hoist 10 mounted on the support beam 8 has a comparatively big diameter, there is still some room for reducing the vertical height of the top space of the elevator shaft 7.
Further, the one end of the hoist cables 13R and 13L are secured to the elevator cage on the side of the counterweight 4 with respect to the center of gravity G of the elevator cage 2, as shown in FIG. 6.
Thus, there is still some room for improving the method of suspending the cage 2 for more stable suspension.
Since the traction pulleys 12R and 12L are on the outer side of the vertical side walls 2R and 2L of the cage 2, respectively, as shown in FIG. 7, an extension shaft 17 needs to be connected to the drive shaft 11R by a coupling 16 when the cage 2 has a big width, which increases the number of parts of the elevator.
Accordingly, it is an object of the present invention to solve those problems in the prior art and to provide an elevator capable of further reducing the vertical height of a top space of an elevator shaft, of further stably suspending a cage, and comprising a reduced number of component parts.
According to a first aspect of the present invention, an elevator includes: a cage capable of vertically moving along cage guide rails in an elevator shaft, and provided on lower surface of its floor with cage-side sheaves; a counterweight capable of vertically moving along counterweight guide rails in the elevator shaft and provided with counterweight-side sheaves; two hoist cables extended in two-to-one roping arrangement around the cage-side sheaves and the counterweight-side sheaves such that one end part of each hoist cable suspends the cage and the other end part of the same suspends the counterweight; and a driving unit including traction sheaves around which the two hoist cables are wound, respectively, and held on upper ends of the counterweight guide rails.
The traction sheaves of the driving unit are disposed in a space between a side surface of the elevator shaft, facing the counterweight and a vertical side surface of the cage facing the same side surface of the elevator shaft when the cage is located at its uppermost position in the elevator shaft.
Since the cage and the counterweight are suspended by the hoist cables extended in two-to-one roping arrangement in the elevator in the first aspect of the present invention, the output torque of the driving unit, as compared with that of a driving unit for an equivalent elevator in which a cage and a counterweight are suspended in one-to-one roping arrangement, may be low and hence the driving unit may be of small dimensions.
Thus, the driving unit can be supported on the upper ends of the counterweight guide rails so that the traction sheaves are in the space between the side surface facing the counterweight of the elevator shaft and the vertical side wall facing the same side surface of the elevator shaft of the cage when the cage of the elevator is located at its uppermost position.
Since the driving unit and the cage do not lie on top of each other, the height of the top space of the elevator shaft may be small.
Since the driving unit and the cage do not lie on top of each other, the height of the top space of the elevator shaft may be small. Since the hoist cables are extended around the cage-side sheaves and the counterweight-side sheaves in two-to-one roping arrangement to suspend the cage and the counterweight, the driving unit can be disposed at a level below that of the ceiling of the cage as located at its uppermost position, so that height of the top space of the elevator shaft may be small.
When the hoist cables are thus extended around the sheaves in two-to-one roping arrangement, the respective moving speeds of the cage and the counterweight are half the winding speed of the traction sheaves; that is, the ratio of the winding speed to the moving speed of the cage and the counterweight is 2 to 1.
In the elevator according to the present invention, the four cage-side sheaves may be disposed respectively at four positions on the lower surface of the floor of the cage, arranged symmetrically with respect to a vertical line passing the center of gravity of the cage, and the two hoist cables wound respectively around the two traction sheaves may be wound around the two cage-side sheaves and around the other two cage-side sheaves, respectively, in two-to-one roping arrangement to support the cage.
In the elevator according to the present invention, the four cage-side sheaves may be disposed respectively at four positions on the lower portion of the cage, arranged symmetrically with respect to a center of gravity of the cage, and the two hoist cables wound respectively around the two traction sheaves may be wound around the two cage-side sheaves and around the other two cage-side sheaves, respectively, in two-to-one roping arrangement to support the cage. Thus, the gravity force and the lifting force both acting on the cage are aligned substantially and hence the cage can be stably suspended.
The center of gravity of the cage in this specification signifies a assumed point on which the gravity force acts when the cage is vacant.
If the cage is designed such that the center of gravity of the cage exists in a rectangle defined by the four cage-side sheaves disposed at the four corners of the cage respectively in top plan view, an offset between the gravity force and the lifting forth both acting on the cage and that is not large and hence the cage can be stably suspended.
Thus, it is preferable to dispose the four cage-side sheaves in the four corners of the floor of the cage, respectively.
In the elevator according to the present invention, ends on the side of the cage of the hoist cables may be connected to a cage-side hitching beam supported on one of the cage guide rails, at positions symmetrical with respect to the cage guide rail which supports the cage-side hitching beam.
Since the hoist cables are extended symmetrically with respect to the cage guide rails and are hitched to the cage-side hitching beam held on one of the cage guide rails symmetrically with respect to the same, bending moments exerted upon the cage-side hitching beam by the two hoist cables respectively, the cage guide rail which support the cage-side hitching beam can be prevented from bending.
In the elevator according to the present invention, the ends on the side of the counterweight of the hoist cables may be connected to counterweight-side hitching devices fixed to a cross beam supported by the counterweight guide rails and the cage guide rail on the side of the counterweight.
Load exerted through the hoist cables on the counterweight-side hitching devices is distributed only to the cage guide rail and the counterweight guide rails and is not distributed to a building in which the elevator is installed.
Since the load exerted through the hoist cables on the counterweight-side hitching devices is distributed to the cage guide rail and the counterweight guide rails, the guide rails are prevented from bending or buckling.